Both the F-22 and F-35 are using gap-fillers, not necessarily any type of RAM paint (FYI, I've seen F-16's painted with RAM paint. It's not that expensive for some levels of stealthy).

Gap-fillers do exactly what they suggest: They fill the gaps in the panel lines etc, thus eliminating radar-reflecting/amplifying cavities on the aircraft surface.

Generally speaking, the aircraft shape + gap fillers form the modern stealth concept.

F-35 gap fillers are newer technology than those of the F-22, and they are being refitted to the F-22, IIRC. This reduces maintenance requirements.

Gap-fillers probably have to be replaced after maintenance (opening and closing of panels).